Method for forming large reinforced foamed plastic panels

ABSTRACT

A method and apparatus for forming large fiber-reinforced foamed plastic panels is disclosed. The panels are produced by a process comprising filling a flat mold with freshly mixed foam plastic precursors, including fibrous material for reinforcement of the panels, closing the mold until the plastic precursors have foamed and set, then opening the mold and removing the finished panel. The apparatus comprises a platen mounted for traversing under the dispensing outlet of a mixing device, whereby the platen is filled with foamed plastic precursors, and a press into which the platen travels before the mixture has begun to mold. The press is provided with a novel mechanism for closing the mold by placing a cover on top of the platen before the plastic begins to foam. The same mechanism is adapted to open the mold by lifting the platen cover. Thereafter, the platen is moved in a reverse of its entry movement, returning to its starting position for removal of the finished panel. The mechanism for opening and closing the mold is operated by hydraulic operators under the supervision of a sequencing controller which provides a tilting movement during operation, providing for expelling of air during closing of the mold and breaking the surface tension between the platen cover and the finished panel by first raising or peeling one corner of the platen so as not to lift the panel out of the mold.

BACKGROUND OF THE INVENTION

In a prior application, Ser. No. 407,829, filed Oct. 19, 1973 ofapplicant and assigned to the assignee of the present application, andnow abandoned, a process was disclosed for forming fiber-reinforcedfoamed plastic articles such as glass fiber reinforced polyurethanearticles. The present application discloses an apparatus for carryingout on a large commercial scale one aspect to that prior processinvention. In U.S. Pat. No. 3,929,318, a mixer is disclosed forpreparing foamed plastic precursors with fiber reinforcement immediatelyprior to dispensing that mixture into a mold where fiber-reinforcedfoamed plastic articles are formed. The above prior application andpatent are related to the present application and are incorporated byreference herein.

The formation of large, flat fiber-reinforced panels in a one-stepprocess is a unique operation, not heretofore carried out commercially.Accordingly, no significant prior art is known which is pertinent to themethod and apparatus for forming such panels as to be disclosed herein.The most important problems to be met in producing these panels may beoutlined as follows.

It is typical of such foamed plastic precursors that within thirtyseconds after being mixed they begin to foam. Accordingly, in thirtyseconds the mold into which the precursors are placed must be completelyfilled and closed. Thus, it is an essential feature of a mold forforming flat panels that it be filled very quickly and uniformly. Inaddition, such a mold must close quickly and at the same time avoidtrapping air inside which could cause substantial defects in the panelswhich are produced. In this regard, it should be noted that in typicalcommercial application panels of approximately 10 feet × 45 feet and 1/4inch and greater thicknesses can be produced. It will be appreciatedthat distribution of foamed material across such an extensive flat areacan be a substantial difficUlty in the formation of such panels. Afterfilling, the mold must also be held closed against the force exerted bythe foaming material in order to create a uniform panel. Since thematerial fills the mold cavity fully, adherence of the panel to the moldbody may cause difficulties. It is essential that the mold be openablewithout damage to the panel.

SUMMARY OF THE INVENTION

A method have been invented for forming large fiber-reinforced foamedplastic panels. The method of forming such panels involves the steps oftransporting a horizontally disposed platen beneath the discharge of amixer for receiving the pre-mixed precursors of the reinforced foamedplastic, including the fiber reinforcement mixed therein. After the moldhas been filled by being transported beneath the discharge of the mixer,it is moved into place within a hydraulic press. There, the platen isclosed by lowering a top onto it in such a manner that air is expelledand thereby forming a closed, flat mold. The mold is kept closed for atime sufficient for the foaming and setting of the plastic precursors,forming a rigid foamed plastic fiber-reinforced panel. After the settingof a panel, the mold is opened by lifting the cover of the platen insuch a manner that no damage to the finished panel results. Thereafter,the platen containing the finished flat panel is transported to aremoval station where the finished panel is lifted from the platen.

In an alternate form of the invention, discharge of the mixer may belocated at one edge of the mold with the top platen already in a closedposition. Thereafter, upon discharge of the foamable plastic mixturefrom the end of the mixer, the mixture will be injected under highpressure throughout the mold cavity to form the finished panel. As inthe previous embodiment, the finished panel may be thereafter removedfrom the mold by lifting of the top mold platen.

Additional features of the method include controlling the time offilling of the platen to the induction period of the foamed plasticmaterial, typically about 30 seconds. In an alternative method of theinvention, the platen is lined with a sheet plastic material toincorporate the plastic material as an additional surface on thefinished flat panel.

An apparatus to be described in more detail hereinafter has beeninvented which will carry out the method of the invention. In oneimportant aspect, the apparatus includes a hydraulic sequencing systemoperating the platen top whereby the top is placed atop and lifted fromthe platen in a tilted or peeling relationship so that air is nottrapped in the mold during closing and so that the surface tensionbetween the panel and top platen is easily broken during mold opening.

The foregoing summary of the invention will be more clearly understoodin light of the detailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a top plan view of the press and platen.

FIG. 2 is a side elevation view similar to that of FIG. 1.

FIG. 3 is a view of the platen taken substantially along line 3--3 ofFIG. 2.

FIG. 4 is a view of the mixer and platen taken substantially along line4--4 of FIG. 3.

FIG. 5 is a top plan view of a modified form of platen for moldingsmaller size panels.

FIG. 6 is a view of the mixer and platen taken substantially along line6--6 of FIG. 5.

FIG. 7 is a sectional view of the press and mold taken substantiallyalong line 7--7 of FIG. 2 during the closing of the platen.

FIG. 8 is an enlarged sectional view of the press during the opening ofthe platen.

FIG. 9 is a sectional detail along line 9--9 of FIG. 7.

FIG. 10 is a cross-sectional view of the panel.

FIG. 11 is an enlarged fragmentary view of the machine of FIG. 2 showingthe film dispenser in more detail.

FIG. 12 is a cross-section of a panel including an integral plastic filmskin.

FIG. 13 is a highly schematic view of the hydraulic system for operatingthe press.

FIG. 14 is an enlarged view of one end of the panel mold of FIG. 11showing the arrangement of the plastic skin about the edge of the panel.

FIG. 15 is a top plan view of one end of the press and platen showing analternate injection method for introducing the foamable plastic into themold.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment will be discussed in connection with acommercially useful apparatus for carrying out the method of theinvention and which can produce large foamed fiber-reinforced flatpanels, which may be in one particular instance 10 feet × 45 feet andone quarter inch and up in thicknesses. When it is considered that sucha panel must be formed in a "one shot" operation wherein a large flatmold is filled with a foamable plastic mixture which will foam in about30 seconds after it is mixed, it will be appreciated that placing thepre-mixed plastic materials within the mold and closing it within a veryshort period of time is extremely critical. Also, it should beunderstood that in a typical embodiment the mixture of foamed plasticprecursors and reinforcing fibers is viscous, thus making difficult thedisposition of the foaming material into the mold. With these problemsin mind, one can proceed to a discussion of the drawings.

FIG. 1 shows a plan view of an apparatus according to the invention forproducing large flat foamed plastic panels containing integralreinforcing fibers. The bottom half of the mold, also called a platen10, is horizontally mounted on tracks 12 on which the platen 10 can betransported into position within the press, shown generally as 14. Atthe beginning of a panel forming cycle, the platen is disposed outsidethe press 14, at the right-hand side of the drawing as indicated. Thepremixed foam plastic precursors will be discharged from a mixer 16mounted near the extreme left end of the platen 10 in FIG. 1. This mixer16 is the subject of a referenced U.S. Pat. No. 3,929,318 where adetailed description may be found. It is sufficient to say here that themixer 16 discharges uniformly mixed foam plastic precursors, includingreinforcing fibers, at a high rate onto the platen 10. The platen 10must be completely filled within approximately thirty seconds since thatis the time in which the foamed plastic will begin to foam in the mold.This short induction period is a severe limitation in the formation ofsuch large panels. According to the invention, the platen 10 istransported horizontally to the left (in FIG. 1) under the mixer 16 andfilled until, at the completion of the fill, the platen 10 has beentransported into position under the press 14. Thereafter, the press 14lowers a top 15 onto the platen 10 in such a manner as to expel airwhich might otherwise be trapped therein and then holds the top closed,forming a closed mold for a flat panel until the plastic materials havefully foamed and set.

FIG. 2 shows an elevation view substantially corresponding to that ofFIG. 1 in which the process just briefly described may be more readilyfollowed. The platen 10, mounted on a wheeled carrier 11 is transportedalong tracks 12 from its starting position under the mixer 16 and intoposition under the press 14. The top 15 is then placed on it by means ofa plurality of hydraulic operators 17 mounted on the upper portion ofthe frame 18. Viewing FIGS. 1 and 2 together, it will be appreciatedthat a substantial frame, typically made of I-beams, supports thetransporting mechanism, the platen 10 and the platen top 15 as well asproviding a rigid frame against which the hydraulic operators may exerttheir force.

Just above the mixer 16 in FIG. 2 an additional feature has been shown,not illustrated in FIG. 1. In an alternative embodiment, the panel maybe covered with a film plastic skin. For this purpose, a roll of film 20is shown mounted on the upper portion 18 of the frame. A further sheetof film 20b is stretched over the bottom of the platen before it isfilled (see FIGS. 11 and 14). As the platen 10 is transported under themixer 16 to receive the premixed foam plastic precursors, the film islaid down over the top of the platen 10 as it is passed into the press14. Once the filling of the platen 10 has been completed, the film canbe cut off after the top has been placed on the press with the filmtrapped in position so that it will appear as a skin on the top, bottomand edges of the finished panel. Thus, the entire panel can be coveredwith a film plastic of material, which is advantageous for someapplications where an integrally bonded sheet plastic surface coating ofany color is desired. Of course, if other surface materials were desiredon the finished panels, a thin metal sheet or foil, fabric, orcomposition sheet could be substituted for the illustrated sheet plasticsurface.

FIGS. 3 and 5 illustrate two alternative forms of the platen of theinvention. The platen of FIG. 3 will produce a simple rectangular flatpanel when it is filled with a mixture of foam plastic precursors havingfiber mixed therein. In FIG. 5, a segmented platen is illustrated havinginternal dividers whereby a panel of varied dimensions may be produced.The platens of FIGS. 3 and 5 are shown in FIGS. 4 and 6, being filled bythe discharge of the static mixer 16 of the referenced invention. Thefoamable plastic mixture is sufficiently resilient so as to spread andfill the mold 10 as illustrated in FIG. 4 when the platen top 15 islowered into place immediately after the foaming cycle is started. Theroller 37 while guiding the top film 20a is also effective to assist inthe spreading of the foamable plastic to the edges of the mold prior toclosing of the platen top 15. The volume of the mixture discharged ontothe large rectangular area of the mold of FIG. 5 will naturally be lessthan that necessary for the FIG. 4 mold due to the reduced size of thepanel made.

FIG. 7 shows in a cross-sectional view the structure and operation ofthe press 14. The surrounding box frame structure 18 is more clearlyseen in this view. The platen 10 in which a foamed panel is formed isillustrated in position within the structure of the press 14. It issupported on I-beams 10a which in turn rest upon other cross beams 10bwhich together form a carriage for transporting the platen 10 from thestarting station into the press. The carriage is mounted upon rollers 22which engage tracks 12 which position and support the platen 10 duringthe panel forming process. The drive motor 23 and cable system 24 may beseen in part also in FIG. 2. This drive means serves to either pull theplaten 10 on its carriage into the press 14 under the discharge end ofthe mixer 16 or, alternatively, moves the platen 10 out of the pressinto the starting position for removal of the finished panel. Such areversal of direction can be accomplished in any number of ways, perhapsthe simplest being use of a motor which electrically reverses direction.

It is necessary to confine the foamable material within the mold whilefoaming takes place and until setting is achieved. This is accomplishedby placing a top 15 over the platen 10. This top 15 may be a simpleplate as shown in FIG. 7, reinforced by I-beams 15a to assure a trulyflat plate, or some other structure might be used. In FIG. 7, crossbeams 15b provide additional rigidity to the top structure. A pluralityof hydraulic operators 26 are attached to these cross beams 15b. Thehydraulic operators 26 move the top 15 and its supporting structure inan up or down movement as necessary to close or open the mold. It willbe clear that trying to place a single large flat sheet 15 over ashallow platen 10 may trap air within the mold, causing discontinuitiesin the finished panel. This air which could be trapped must be released.According to the invention, a method of accomplishing this is to lowerthe top 15 with one edge lower than the other. In such an attitude thelower edge of top 15 will touch the platen 10 first. Then the top islowered into position and sweeps out the air which could be trappedwithin the platen. Individual control of the hydraulic operators 26makes this possible. Because of the extremely rapid induction period,after which the foaming begins to take place, it has been founddesirable in forming such large panels for the narrow end of the panelwhich first enters the press to be contacted first with the top 15 sothat the end of the platen in which foaming begins is covered first.Accordingly, a portion of the platen 10 which enters the press last,that is the opposite end, is covered last just before the foamingprocess begins. By proper programming of the hydraulic operators 26 itis possible to achieve such a selective closing of the top onto theplaten 10 to achieve a closed mold. In practice it has been founddesirable to start closing of the mold by lowering one corner of the topplate first and finish the closing of the mold by closing the diagonallyopposite corner of the plate 15 last. The great force that can beapplied by the activators 26 in this way will assure that the moldcharge is quickly and uniformly squeezed into all four corners and sidesof the mold prior to and during the time that the chemical foamingreaction takes place. The hydraulic operators 26, being mounted on theupper cross beams 15b of the surrounding box frame 14 are able to exerta force against the frame 14 in raising or lowering the platen top 15.The hydraulic system 30 has typically placed atop the surrounding boxstructure, a portion of which may be seen in FIG. 7.

While the mold is closed by setting the platen top 15 down one edge orcorner first and then lowering the remainder of the top 15, a somewhatsimilar process occurs during the removal of the top 15 after theformation of the foamed panel. This is illustrated in FIG. 8. One edgeor corner of the platen top may be lifted first. This has the doubleadvantage of preventing damage to the panel and at the same timereducing the amount of effort required in order to lift the top. It willbe appreciated that if the mold is completely full, as it will be afterthe panel is set, that the air pressure on top of the platen top will besubstantial and a vacuum could be created in attempting to lift the topwhich would require a very large force to overcome. By lifting one edgeinstead, any potential vacuum is broken by the in-rush of air and it ispossible to lift the top 15 solely against its own weight with a littleresistance from the adhesion of the panel to the platen top. Again, asin FIG. 7, the operation of FIG. 8 requires a coordinated programming ofthe operation of the hydraulic operators 26 which is illustrated in aschematic control diagram, FIG. 13.

FIG. 9 illustrates a semi-ball and socket construction used at the endof the hydraulic operators which permits the unequal applying of forceas is required for the programmed lifting of the platen top. Theoperator shafts obviously can only move in a vertical direction. If, asin FIG. 8, for example, the left-hand operator 261 is to move upwardwhile the right operator 26r is to have little or no movement it isnecessary that the connection of the operators shafts 271 and 27r to thesupporting beams 15b must be flexible in nature. This is provided by thestructure shown in FIG. 9 wherein a curved ball and socket member 28 isfree to move to accommodate the angle developed by the top 15 as it islifted from one side.

In FIG. 10, a cross-section of a finished panel 32 is shown. This panelwill contain distributed reinforcing fibers throughout the rigid mixturedisposed therein as desired and established by the conditions underwhich the materials are mixed. This fiber distribution in the foamedpanel is the general subject of application Ser. No. 407,829 to whichreference has been made. Such a panel is useful for many applications.However, as previously mentioned, there may well be applications inwhich an integral plastic film 33 serving as the skin of such a panelwould be desirable. Such applications would, for example, be fordecorative structural building panels or tractor trailer roof and sidepanels where high strength, durability and appearance is desired.

Formation of such skinned panel has been discussed previously inconnection with FIG. 2.

FIG. 11 illustrates in more detail the plastic film dispensing meanswhich was discussed in connection with FIG. 2. The film 20a can beclamped in place on one edge of the platen 10 by clamp 34 and thensimply pulled out as the platen 10 is horizontally transported beneaththe mixer 16 and into position in the press. In the illustration of FIG.11, it will be observed that the platen 10 is first covered with abottom sheet of stretched film 20b and subsequently positioned in thepress 14 as the platen 10 is completely covered by the stretched film20a. At this point the platen 15 will be lowered onto the platen 10 toclose it and form a closed mold. Thereafter, the film may be cut offduring the setting period.

FIG. 13 schematically illustrates the control system by which thehydraulic operators 26 are programmed sequentially and activated inorder to accomplish the tilted attitude required during the raising andlowering of the platen top 15 as previously described. The arrangementof FIG. 13 includes a programmed hydraulic controller or sequencingmechanism 35 connected to the actuators 26 by a plurality of pressureand return lines 36. The necessary hydraulic pressure is supplied by apump 38 connected to a fluid reservoir 40. The controller 34 will beunderstood to include all the necessary valves, timing devices, etc. toaccomplish the desired programmed upward and downward actuation of theoperators 26 during the panel molding cycle.

FIG. 14 shows an enlarged end section of the bottom leading edge of theplaten to better show a manner in which the upper and lower plasticsheets 20a and 20b are secured with an end slip 34. In practice, ifdesired, the bottom sheet 20b may be stretched over the platen 10 andsecured thereto with the use of masking or adhesive tape or any othersuitable means.

In FIG. 15, an alternate form of foamable plastic introduction means isshown. In this embodiment, the same mixer nozzle 16 as is shown in thefirst embodiment has been relocated to the left end of the machine shownin FIG. 1 and arranged to directly inject the plastic mixture into themold cavity. In this arrangement, the injection would naturally onlycommence with the mold in a closed position, and during injection thetrapped air in the mold would be expelled from the opposite end or fromadditional vents which could be placed about the edges of the moldcavity as required.

The foregoing description of the preferred embodiment is forillustration and explanation of the invention and should not beconstrued to limit the scope thereof which is defined by the claimswhich follow:

What is claimed is:
 1. A method of forming a large flat foamed plasticpanel from a foamable thermosetting resin reaction mixture which willfoam in about 30 seconds after said mixture is formed comprising thesteps of:(a) transporting an open horizontally disposed mold having araised boundary edge defining a cavity therein beneath the discharge ofa mixer while said mixer discharges the foamable mixture into the cavityof said mold within about 30 seconds, the amount of resin mixturedischarged being sufficient that upon foaming the foamed resin will fillthe mold; (b) continuing the transport of said mold past the dischargeend of said mixer to place said mold in position within an adjacentmolding press having a mold cover therein; (c) lowering said mold coveratop said mold into contact with said raised boundary edge therebyforming a closed flat mold, said lowering being effected progressivelybeginning first at one corner of the end of the mold first transportedinto the molding press and continuing diagonally toward the opposite endthereof by a plurality of sequentially activated operators wherebytrapping of air thereunder is prevented; (d) holding the mold closed fora time sufficient for foaming and setting of the foamable mixture; (e)raising the cover from contact with the raised boundary edge, saidraising being initiated at one corner of said mold and continuingdiagonally to the opposite end thereof by a plurality of sequentiallyactivated operators to progressively peel the cover from said panelwhereby damage to the foamed panel is prevented; and (f) returning theopened mold to its initial position.
 2. A method of forming a largefiber reinforced foamed plastic flat panel comprising the steps of:(a)transporting a horizontally disposed mold having a cavity thereinbeneath the discharge of a mixer; (b) discharging from said mixer intosaid mold cavity a foamable thermosetting resin reaction mixturecontaining fibers intermixed therein while said mold is transported bystep (a), the amount of foamable resin mixture discharged beingsufficient that upon foaming the foamed resin will fill the mold, saiddischarging being completed before foaming of the resin takes place; (c)continuing the transport of the mold of step (a) until said mold ispositioned within a molding press, having a mold cover therein; (d)lowering the mold cover atop said mold thereby forming a closed flatmold, said lowering being effected progressively beginning first at theend of the mold first transported into the molding press and continuingtoward the opposite end thereof by a plurality of sequentially activatedoperators whereby trapping of air thereunder is prevented; (e) holdingthe mold of step (d) for a time sufficient for foaming and setting ofthe foamable mixture of step (b) to form a rigid foam fiber reinforcedpanel; (f) opening said closed mold by lifting the corner of said moldcover lowered in step (d), said lifting being initiated at one corner ofsaid mold and continuing to the opposite end thereof by a plurality ofsequentially activated operators to progressively peel the cover fromsaid mold whereby damage to the foam panel is prevented; (g)transporting said open mold of step (f) to the initial position of (a);and (h) removing the panel of step (e) from said mold.
 3. The method ofclaim 2 wherein the time of discharging said mixer is about 30 seconds.4. The method of claim 2 further comprising the step of lining thebottom of said mold with plastic film prior to the discharge of theresin mixture into the mold.
 5. The method of claim 2 further comprisingthe step of covering the foamable mixture after the discharge thereof ofstep (b) with a plastic film and prior to the closing of the mold ofstep (d).